Our laboratory is interested in defining the differential contribution made by specific subpopulations of keratinocytes to the formation of papillomas and carcinomas after exposure to a single topical application of a chemical carcinogen followed by repeated exposure to 12-0-tetradecanoylphorbol-13- acetate (TPA). Our hypothesis is that TPA differentially stimulates keratinocytes subpopulations in the skin. These subpopulations make distinctly different contributions to tumor formation. We have identified several distinct subpopulations of epidermal cells, including a population of small, dense cells present only in TPA treated mice that is characterized by enhanced functional and biochemical reactivity. This subpopulation of keratinocytes produces significant amounts of reactive oxygen intermediates as well as Interleukin-1 (IL-1), an inflammatory mediator. A smaller, less granular keratinocyte subpopulation rapidly proliferates in response to TPA treatment, and at later stages in the tumor promotion process, has high constitutive expression of ODC. This subpopulation may contain cells that ultimately form papillomas and carcinomas. The goal of the proposed studies is to integrate the potential respective roles of reactive oxygen intermediates and Interleukin-1 produced by subpopulations of keratinocytes with the expression of ODC and the growth of papillomas and carcinomas that also arise from a (possibly) different subpopulation of keratinocytes. We have developed new techniques that combine cell sorting technology and Northern blotting procedures that allow detection of mRNA transcription levels of ODC and IF-1 in specific keratinocyte subpopulations following short and long term TPA treatment in order to gain a better understanding of the molecular and cellular basis for tumor promotion and progression.